The present invention relates generally to coolant manifolds and, in particular, to plastic coolant manifolds that are used in electric vehicles (both electric and hybrid electric vehicles) to supply coolant to and from a power electronics module within the vehicle.
Electric vehicles typically utilize an inverter in the form of a switch-mode power supply to provide three phase operating power to the vehicle""s electric drive motor. Because of the torque demands on the electric motor, the inverter includes a number of power switching devices that can supply the high currents needed. The inverter is usually located in an environmentally sealed module that is commonly referred to as the power electronics bay (PEB). This module typically includes other electronic circuits, such as those used to run the vehicle""s electronic power steering, climate control compressor motor, and traction control system.
In an effort to minimize the amount of electromagnetic interference (EMI) radiated from the inverter and other circuitry within the power electronics bay, the circuits themselves are enclosed together within a grounded metal chassis. This chassis normally includes a housing having feedthrough electrical connectors (for power, control, and data signals) as well as an inlet and outlet coolant manifold that permit liquid coolant to be circulated through the power electronics bay for cooling of the inverter""s power switching devices. In a typical liquid-cooled inverter application, the power switching devices are mounted by their baseplates to a conductive metallic liquid-interface heat exchanger. The coolant manifold of the heat exchanger that leads into and out of the chassis is metallic and is attached to the chassis. Thus, there is no electrical isolation at the interface between the switching devices and the heat exchanger, and at the interface between the heat exchanger and chassis. Consequently, the baseplates of the power switching devices are electrically connected to both the coolant and chassis, resulting in capacitive coupling between the power switching devices and the chassis that can be as much as 190 pF or more. This allows undesirably high currents to be injected into the chassis, resulting in unwanted radiated emissions.
Accordingly, there exists a need for a power electronics liquid coolant system that reduces the radiated EMI due to currents flowing from the switching devices through the coolant and into the chassis.
In accordance with the present invention, there is provided an improved enclosure for a liquid-cooled power electronics module of an electric vehicle. The enclosure comprises a power electronics chassis that includes a metal or otherwise electrically conductive housing and a plastic or otherwise electrically non-conductive manifold for providing coolant flow into the housing. The housing has at least one wall that includes an outer surface and a recessed aperture that provides access to an interior region of the housing via a passageway. The passageway is defined by an axial wall of the housing that extends towards the interior region from the outer surface of the housing to the aperture. The manifold has an inlet that extends through the passageway in contact with the housing. The inlet has an internal passage that is spaced from the axial wall by a first distance and that is spaced from the aperture by a second distance, with the first distance being greater than the second distance.
This configuration not only provides electrical isolation of the coolant from the chassis, but does so in a manner that significantly reduces the capacitive coupling between the coolant and chassis. As a result, when used for an electric vehicle power electronics module containing an inverter for the vehicle""s electric drive motor, the invention significantly reduces the radiated EMI outside of the chassis, as compared to conventional chassis-manifold constructions.
Preferably, the aperture and passageway have a circular cross-sectional shape with the aperture being defined by an annular wall having a diameter that is less than the diameter of the passageway. Preferably, the outer surface and internal passage of the inlet have a circular cross-sectional shape and are uniform along their lengths, with the outer surface of the inlet only contacting the housing at the aperture. This provides a gap between the inlet and inner wall of the passageway that helps reduce capacitive coupling between the coolant and chassis.